A mechanics stethoscope reveals so much..
And a long screw driver held hard to the ear like a stethoscope reveal almost as much..
Either will local if lifter or tappets and which ones...
Also do it with tappet covers on....it is not unheard of to panic without counting to10 very slowly 1st , only to find a tappet gasket has shrunk slightly and a tappet is just touching it.. and it may not even leave a mark.. or touch at idle.
Yep measure the height lift as mentioned above...both at the lifter/ push rod and the tappet and compare to others and the cam spec.
Cams bearing etc MUST be run in on the manufactures install instructions which include the lubes...
I run a oil change after about 50/100 miles and never have used aftermarket oil additives...ESPEC on a new engine.... the oil companies spend millions on research, avoiding big court cases ... and we think we know different... or simply once again sucked into the Goebbels marketing propaganda BS....
First I checked the oil. It was somewhat low,........The motor has about 2500-3000 miles on it and was broken in properly.
These 2 snippets of info are interesting thu... I assume the engine was oprginally fired up run in... then oil levels checked and topped up if needed , or changed, and refilled to correct levels ???? For the level to drop that far in that many miles I wounder if the rings have bedded in , or maybe a collapsed and/or cracked piston skirt?
If what sounds like a lifter/ tappet but have difficulty locating the sound source with a stethoscope.... including from under the car on a hoist....
you have a big carb, most properly not ball park dialed in, when firing up someone most properly swinging on the dizzy to get it to fire, fires , they leave it there rather than retard a bit... take the rpms up to bed rings cam etc, over advanced , and rich... big heat in pistons and one grabs a wall....Often the tap is not heard for some time/ miles later.
Hopefully not check out the other stuff 1st.
But that low oil is a worry.